The present invention relates to a tip of a ball point pen and, more particularly, to a writing tip including a ball rotatably received by a ball supporting seat of a plastic held within a ball receiving hole of a metallic tip body and to a method of making the same.
With the recent increase of the use of aqueous ink instead of oil based ink, it has become essential to use a ball supporting seat which is made of a plastic and precisely held in a ball receiving hole drilled at one end of a metallic tip body. When aqueous ink is applied to a ball point pen wherein the ball is directly supported by a bottom surface of the ball receiving hole, a breakage of thin film of the aqueous ink formed on the ball surface easily occurs when writing pressure is exerted on the ball, due to the relatively low viscosity of aqueous ink compared with that of oil ink. This causes undesirable noise and deterioration of the wear-resistance of the ball and the ball supporting surface. Such drawbacks are avoided by using a ball supporting seat of plastic which has a certain degree of elasticity.
The size of the ball used in current popular ball point pens is in general 1.0 mm, and is typically 0.5 mm or less in those pens for writing extremely thin lines. Therefore, the ball supporting seat of plastic must be correspondingly very small in size and very thin. At the same time, the seat must be firmly secured in the ball receiving hole of the tip body so as not to be moved, in order to ensure a smooth rotataion of the ball.
Although an effort has been made to firmly secure the ball supporting seat within the ball receiving hole by using an adhesive, such solution has been found inconvenient in that an excessive adhesive causes a clogging of ink flowing passage such as an ink guiding groove, while the mechanical bonding strength obtained thereby is not so large. In addition, it is quite difficult to insert the prefabricated supporting seat into the ball receiving hole, which makes the mass-production of the ball point pen difficult and troublesome.